CA1130260A - Agglomeration type coal cleaning processes - Google Patents
Agglomeration type coal cleaning processesInfo
- Publication number
- CA1130260A CA1130260A CA348,868A CA348868A CA1130260A CA 1130260 A CA1130260 A CA 1130260A CA 348868 A CA348868 A CA 348868A CA 1130260 A CA1130260 A CA 1130260A
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- Canada
- Prior art keywords
- coal
- fluorocarbon
- agglomerates
- promoting additive
- agglomeration
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
Coal recovery processes of the agglomeration type in which solvent extraction with a fluorocarbon solvent is used to recover the agglomeration promoting additive.
Coal recovery processes of the agglomeration type in which solvent extraction with a fluorocarbon solvent is used to recover the agglomeration promoting additive.
Description
~3~ 3 AGGLOMERATION TYPE COAL CLEANING PROC~SSES
This invention relates to processes for re-covering coal in a commercially valuable form. It relates, more specifically, to novel, improved processes of that character in which an agglomeration promoting additive is employed in conjunction with mechanical action to effect the separation of coal particles from mineral matter associated therewith in a slurry and the subsequent coales-cence of those particles into flocs or agglomerates which can be recovered from the slurry.
Certain terms used herein are deEined as follows:
Raw coal -- a composite oE coal and mineral matter, a term used herein for the sake of convenience -to include impurities other than inorganic material associated with coal. In general, raw coal will constitute the feed-stock for a process designed to remove mineral matter there-from. The raw coal may be as mined with or without having been subjected to preliminary preparation; or it may be the black water from a hydrobeneficiation plant or the culm from a sludge pond, etc.
Product coal -- the carbonaceous coal phase generated in and recovered from a specified cleaning process.
Processes of the character described above, using liquid hydrocarbons as an agglomeration promoting additive, have been available for at least sixty years.
Such processes are disclosed in Convertol Process, .~
~13~Çi0 Brisse et al, MINING ENGINEERING, February 1958, pp. 258- 261;
AGGLOMERATION 77, Vol. 2, K.V.S. Sastry, Ed., American Institute of Mining, Metallurgical & Petroleum Enyineers, Inc., New York, New York, 1977, chapters 54-56, pp. 910-951;
and in U.S. Patents Nos. 2,74~,626 issued December 15, 1952, to Reerink et al; 2,769,537 issued November 6, 1956, to Reerink et al; 2,769,538 issued November 6, 195~, to Reerink et al; 2,781,904 issued February 19, 1957, to Reerink et al;
This invention relates to processes for re-covering coal in a commercially valuable form. It relates, more specifically, to novel, improved processes of that character in which an agglomeration promoting additive is employed in conjunction with mechanical action to effect the separation of coal particles from mineral matter associated therewith in a slurry and the subsequent coales-cence of those particles into flocs or agglomerates which can be recovered from the slurry.
Certain terms used herein are deEined as follows:
Raw coal -- a composite oE coal and mineral matter, a term used herein for the sake of convenience -to include impurities other than inorganic material associated with coal. In general, raw coal will constitute the feed-stock for a process designed to remove mineral matter there-from. The raw coal may be as mined with or without having been subjected to preliminary preparation; or it may be the black water from a hydrobeneficiation plant or the culm from a sludge pond, etc.
Product coal -- the carbonaceous coal phase generated in and recovered from a specified cleaning process.
Processes of the character described above, using liquid hydrocarbons as an agglomeration promoting additive, have been available for at least sixty years.
Such processes are disclosed in Convertol Process, .~
~13~Çi0 Brisse et al, MINING ENGINEERING, February 1958, pp. 258- 261;
AGGLOMERATION 77, Vol. 2, K.V.S. Sastry, Ed., American Institute of Mining, Metallurgical & Petroleum Enyineers, Inc., New York, New York, 1977, chapters 54-56, pp. 910-951;
and in U.S. Patents Nos. 2,74~,626 issued December 15, 1952, to Reerink et al; 2,769,537 issued November 6, 1956, to Reerink et al; 2,769,538 issued November 6, 195~, to Reerink et al; 2,781,904 issued February 19, 1957, to Reerink et al;
2,842,319 issued`July 8, 1958, to Reerink et al; 3,0~5,818 issued July 24, 1972, to Muschenborn et al; 3,26~,071 lssued April 23, 1966, ko Puddington et al; 3,637,464 issued January 25, 1972, to Walsh; and 4,033,729 issued July 5, 1977, to Capes et al.
One disadvantage oE kh~s prior art process is that the recovery of even a part of the agglomeration promot-ing additive requires that the product coal agylomerates be heated at a temperature of 250-350C (482-662F). This is economically unattractive. Furthermore, temperatures of the magnitude in question can cause unwanted changes in the composition of the product coa].
Because of the cost of, and ~roblems involved in, recovering agglomeration promoting additives of -the conven-tional type, they have hereto~ore apparently, for the most part, simply been left on the product coal.`and lost to the process. At the current elevated prices of the hydrocarbons employed as agglomerating agents, this can make the above-described coal cleaning process economically unattractive.
We have now discovered that, unexpectedly, the - agglomeration promoting additive can be recovered from the 1~3~
; product coal generated by the process in question at a low enough cost and with a degree of efficiency which makes the process commercially attractive. More particularly, we have found that this novel, and important, objective can be attained by washing the product coal agglomerates with certain halogenated derivatives of methane and ethane which prove to have a high solvent power for the conventional additives. The solvent is then separated from the additive, and both compositions are recycled.
Those solvents which we consider suitable for use in the novel process just described because of their high solvent power, low latent heat of vaporization, low viscosity and surface tension and their chemical inertness toward coal and materials emplo~ed in the process equipment are certain fluorinated derivatives of methane and ethane; i.e., compos:i-tions of the class generally designated by the generic form "fluorocarbons". Useful fluorocarbons include:
l-Chloro-2,2,2-trifluoroethane 1,1-Dichloro-2,2,2-trifluoroethane Dichlorofluoromethane l-Chloro-2-fluoroethane 1,1,2-Trichloro-1,2,2-trifluoroethane 1,1-Dichloro-1,2,2,2-tetrafluoroethane Trichlo.ofluoromethane ~ixtures of the foregoing compounds can also be employed.
Of the listed compounds~ all but the last three are at the present time probably too expensive to be practical from an economic viewpoint. And, of the latter, ~3~
1,1,2-trichloro-1,2,2-trifluoroethane and trichlorofluoro-methane are preferred because of their optimum physical properties, lack of chemical activity, and relatively low cost.
The boiling points of the fluorocarbons we employ are relatively low. Because of this and their Iow latent ~;
heats of vaporization, they can be separated from the agglomeration promoting additive which they strip from the product coal agglomerates at a modest cost. Recovery rates approaching 100 percent are easily attained.
Also, the fluorocarbons we employ in the novel process described above do not form azeotropes with moisture associated with the product coal to any commercially signifi-cant extent. This is important because azeotropes can be resolved into their components only at relatively high cost.
~et another advantaye of our novel process is that the separation of the fluorocarbon solvent from the ; agglomeration promoting additive can be carried out at ambient temperature and pressure or at temperatures and pressures approaching ambient.
Still another important advantage of our inven-tion, alluded to above, is that the fluorocarbons employed to recover the agglomeration promoting additives do not react chemically with coal under the process conditions we employ. This is important because contaminated coals are undesirable. In the case of steaming coals chemical con-- taminants can cause boiler corrosion. Contaminated coking coals can alter the chemistry of the reactions in which they are employed in unwanted directions.
Chemical contamination may also make it necessary ~3~26~
to purify the fluorocarbon and/or the agglomera-tion promoting additive before they are recycled to the process. This, potentially, makes the entire process economically unattrac-tive.
Furthermore, because the fluorocarbons we employ are chemically inert under process conditions, our novel process can be carried out without generating the pollutants attributable to many coal cleaning processes.
From the foregoing, it will be apparent to -the reader that the primary objec-t of the present invention resides in the provision of novel, improved methods for separating coal from mineral matter associated therewith.
Another important but more specific object of the invention resides in the provision of a process of the character just described in which an additive is introduced into an aqueous slurry of the raw coal to promote the separation of the coal particles from the mineral matter associated therewith and the coalescence of said coal into agglomerates and in which provision is made for subse~uently - recovering the agglomerati~n promoting additive from the product coal agglomerates.
Other important but still more specific objects o our invention reside in the provision of processes.in accord with the preceding object in which:;
the agglomeration promoting additive can be recovered from the product coal agglomerates with only a modest, commercially viable eY~penditure of energy;
the agglomeration promoting additive can be recovered from the product coal agglomerates without generat-3C ing ecologically undesirable wastes;
- 5 ~
3L3~3~ 3 the agylomeration promoting additive can be recovered from the product coal agglomerates under conditions which are, or approach, ambient, thereby eliminating the safety and other problems appurtenan-t to the use of high temperatures and/or non-atmospheric pressures.
Still ano-ther important object of the present invention resides in the provision of coal cleaning processes which employ a soluble ag~lomeration promoting ad~itive alld in which the additive is recovered from thc product coal agglomerates by washing the agglomerates wi-th a fluorocarbon in which the additive is soluble, mechanical].y se~arating the fluorocarbon and additive from the agcJlomerates, separating the ~luorocarbon from the a~glomeration promo~incJ adclitive, and recycling bo-th the fluorocarbon and the additive.
P~elated, but more spec~fic, objects o~ our inven-tion reside in the provision of processes in accord with the preceding object:
which employ a fluorocarbon that can be separated from the a~glomeration promot.in~ additive by evaporation and then purged oE non-condensible gases, condensed, and recycled Witil only modest expenditures of ener~y;
which employ a fluorocarbon that has high solvent power and low viscosity, surface tension, and latent hcat of vaporization and which is chemically inert with respect to coal under the process conditions;
which employ fluorocarbons that are non-flammable, odor free, non-corrosive, and non-toxic.
Those objects are broadly a-ttained by the invelltion which contemplates a process for recovering coal from a particulate composite in which the coal is associated w.it~
mineral matter and which comprises the steps of treating the composite in an aqueous carrier with a non-aqueous, organic agglomeration promo-ting additive wi-th respect to which the coal is hydrophobic to effect a coalescence of the coal particles into product coal agglomerates, and the e~ection of mineral matter into dispersion in the aqueous carrier. The product coal agglomerates are recovered from the aqueous carrier, and the product coal agglomerates are washed with a fluorocarbon in which the additive is soluble to thereby effect a recovery of the agylomeration promoting additive from the product coal agylomerates.
O-ther important objects, advantages, and features of the present inven-tion will be apparen-t from the foregoing and the appended claims and as the ensuing detailed
One disadvantage oE kh~s prior art process is that the recovery of even a part of the agglomeration promot-ing additive requires that the product coal agylomerates be heated at a temperature of 250-350C (482-662F). This is economically unattractive. Furthermore, temperatures of the magnitude in question can cause unwanted changes in the composition of the product coa].
Because of the cost of, and ~roblems involved in, recovering agglomeration promoting additives of -the conven-tional type, they have hereto~ore apparently, for the most part, simply been left on the product coal.`and lost to the process. At the current elevated prices of the hydrocarbons employed as agglomerating agents, this can make the above-described coal cleaning process economically unattractive.
We have now discovered that, unexpectedly, the - agglomeration promoting additive can be recovered from the 1~3~
; product coal generated by the process in question at a low enough cost and with a degree of efficiency which makes the process commercially attractive. More particularly, we have found that this novel, and important, objective can be attained by washing the product coal agglomerates with certain halogenated derivatives of methane and ethane which prove to have a high solvent power for the conventional additives. The solvent is then separated from the additive, and both compositions are recycled.
Those solvents which we consider suitable for use in the novel process just described because of their high solvent power, low latent heat of vaporization, low viscosity and surface tension and their chemical inertness toward coal and materials emplo~ed in the process equipment are certain fluorinated derivatives of methane and ethane; i.e., compos:i-tions of the class generally designated by the generic form "fluorocarbons". Useful fluorocarbons include:
l-Chloro-2,2,2-trifluoroethane 1,1-Dichloro-2,2,2-trifluoroethane Dichlorofluoromethane l-Chloro-2-fluoroethane 1,1,2-Trichloro-1,2,2-trifluoroethane 1,1-Dichloro-1,2,2,2-tetrafluoroethane Trichlo.ofluoromethane ~ixtures of the foregoing compounds can also be employed.
Of the listed compounds~ all but the last three are at the present time probably too expensive to be practical from an economic viewpoint. And, of the latter, ~3~
1,1,2-trichloro-1,2,2-trifluoroethane and trichlorofluoro-methane are preferred because of their optimum physical properties, lack of chemical activity, and relatively low cost.
The boiling points of the fluorocarbons we employ are relatively low. Because of this and their Iow latent ~;
heats of vaporization, they can be separated from the agglomeration promoting additive which they strip from the product coal agglomerates at a modest cost. Recovery rates approaching 100 percent are easily attained.
Also, the fluorocarbons we employ in the novel process described above do not form azeotropes with moisture associated with the product coal to any commercially signifi-cant extent. This is important because azeotropes can be resolved into their components only at relatively high cost.
~et another advantaye of our novel process is that the separation of the fluorocarbon solvent from the ; agglomeration promoting additive can be carried out at ambient temperature and pressure or at temperatures and pressures approaching ambient.
Still another important advantage of our inven-tion, alluded to above, is that the fluorocarbons employed to recover the agglomeration promoting additives do not react chemically with coal under the process conditions we employ. This is important because contaminated coals are undesirable. In the case of steaming coals chemical con-- taminants can cause boiler corrosion. Contaminated coking coals can alter the chemistry of the reactions in which they are employed in unwanted directions.
Chemical contamination may also make it necessary ~3~26~
to purify the fluorocarbon and/or the agglomera-tion promoting additive before they are recycled to the process. This, potentially, makes the entire process economically unattrac-tive.
Furthermore, because the fluorocarbons we employ are chemically inert under process conditions, our novel process can be carried out without generating the pollutants attributable to many coal cleaning processes.
From the foregoing, it will be apparent to -the reader that the primary objec-t of the present invention resides in the provision of novel, improved methods for separating coal from mineral matter associated therewith.
Another important but more specific object of the invention resides in the provision of a process of the character just described in which an additive is introduced into an aqueous slurry of the raw coal to promote the separation of the coal particles from the mineral matter associated therewith and the coalescence of said coal into agglomerates and in which provision is made for subse~uently - recovering the agglomerati~n promoting additive from the product coal agglomerates.
Other important but still more specific objects o our invention reside in the provision of processes.in accord with the preceding object in which:;
the agglomeration promoting additive can be recovered from the product coal agglomerates with only a modest, commercially viable eY~penditure of energy;
the agglomeration promoting additive can be recovered from the product coal agglomerates without generat-3C ing ecologically undesirable wastes;
- 5 ~
3L3~3~ 3 the agylomeration promoting additive can be recovered from the product coal agglomerates under conditions which are, or approach, ambient, thereby eliminating the safety and other problems appurtenan-t to the use of high temperatures and/or non-atmospheric pressures.
Still ano-ther important object of the present invention resides in the provision of coal cleaning processes which employ a soluble ag~lomeration promoting ad~itive alld in which the additive is recovered from thc product coal agglomerates by washing the agglomerates wi-th a fluorocarbon in which the additive is soluble, mechanical].y se~arating the fluorocarbon and additive from the agcJlomerates, separating the ~luorocarbon from the a~glomeration promo~incJ adclitive, and recycling bo-th the fluorocarbon and the additive.
P~elated, but more spec~fic, objects o~ our inven-tion reside in the provision of processes in accord with the preceding object:
which employ a fluorocarbon that can be separated from the a~glomeration promot.in~ additive by evaporation and then purged oE non-condensible gases, condensed, and recycled Witil only modest expenditures of ener~y;
which employ a fluorocarbon that has high solvent power and low viscosity, surface tension, and latent hcat of vaporization and which is chemically inert with respect to coal under the process conditions;
which employ fluorocarbons that are non-flammable, odor free, non-corrosive, and non-toxic.
Those objects are broadly a-ttained by the invelltion which contemplates a process for recovering coal from a particulate composite in which the coal is associated w.it~
mineral matter and which comprises the steps of treating the composite in an aqueous carrier with a non-aqueous, organic agglomeration promo-ting additive wi-th respect to which the coal is hydrophobic to effect a coalescence of the coal particles into product coal agglomerates, and the e~ection of mineral matter into dispersion in the aqueous carrier. The product coal agglomerates are recovered from the aqueous carrier, and the product coal agglomerates are washed with a fluorocarbon in which the additive is soluble to thereby effect a recovery of the agylomeration promoting additive from the product coal agylomerates.
O-ther important objects, advantages, and features of the present inven-tion will be apparen-t from the foregoing and the appended claims and as the ensuing detailed
3 ~3~
description and discussion proceeds in conjunction ~ th the appended drawing in which the single figure is a flow diagram of one process for beneficating coal in accord with the principle of the present invention.
Referring now to the drawing, the separation of coal from the mineral matter associated therewith, the sub-sequent agglomeration of the coal particles, and the ejection of mineral matter and water from the agglomerates is carried out in an agglomerator 10 which may be, for example, a homogenizer as described in U.S. Patent ~o. 2,744,626 issued ~ .
December 15, 1952, to Reerink et al; a tumbler as described in U.S. Patent No. 3,471,267 issued October 7, 1965, to Capes et al; or a ball, beater, buhr, cage, Chilean, colloid, disc, distintegrating, hammer, pebble, pendulum, pin, Raymond, rod, or comparable mill.
The separation may be carried ou-t at ~mbient temperature and pressure.
Agglomerator 10 p~ovides mechanical forces which jam the coal particles in the raw coal into agglomerates of - the wanted character and which eject the mineral matter and water from the agglomerates. In addition, it generates .forces which knead or work the agglomerates to expel addi-tional mineral matter and water therefrom.
Also, if a mill type agglomerator is employed, the agglomerator reduces the size of the material fed to it, perhaps liberating additional product coal from the mineral matter to which it is bound, and exposing fresh surfaces on the coal particles. Exposure of fresh surfaces to the agglomerating agent can be important because the agglomera-tion of the product coal particles involves surface active , 2F~6~
phenomena which~ at least generally, operate most efficiently only on freshly exposed coal particle surfaces.
Raw coal and the selected agg]omeration promoting additive are introduced into agglomerator 10 through transfer devices indicated generally by reference characters 12 and 14. Such water as may be necessary to form a slurry wi-th appropriate characteristics is introduced into mill 10 through conduit 16.
The amount of additive we employ is th.~t necessary for an efficient agglomeration o the particles of product coal to be effected. As discussed in the reerences cited above, this can range from G0 to over 200 pounds of additive per ton of coal.
As indicated above, the additive employed in ou~
novel process is a hydrocarbon whlch is soluble in the fluorocarbon used -to recover it. The addi-tive, which must be one with respect to which the coal particles are hydrophobic, will typically be, or include:, a petroleum distillate or solvent; a nitrobenzene; a kerosene; a lubricating, fuel, or residual oil; or a chlorinated biphenyl.
As discussed in copending Cdn. Serial No. 33g,~11, iled November 2, 1979, it is also desirable, in many cases, to add calcium oxide in either hydrated or anhyclrous form to the slurry during the agglomeration process. The calci.um oxide, if employed, is introduced into agglomerator 10 through transfer device 17. From 0.5 to 3 percent of calcium oxide (calculated as CaO) based on the weight of the raw coal is employed. It is preferred that the calcium oxide be dosed or metered to the agglomerator over the period of coal ~30 particle separation and agglomeration.
g _ , . . _ ~ .
-~ 3 3 ..:
Tlle ac~ueous carri~r and mineral mat-ter are dis-charged- from agglol~erator 10 through a screen 18 on which the agglomerates of product coal are retained. This aclueous phase is transferred through conduit 20 to a conventlonal thickener (not shown). Suitable thickeners ~re described in Taggart, HANDBOOK OF MI~ERAL DR~SSING, John r.~iley & Sons, Inc., New York, New ~or~, 1927, pp. 15-0~ -- 15-~6~ rrhe mineral matter consol~da-ted in -the -thickener may be transferred to a refuse heap or landfill, for example;
and the water can be recycled.
Up to 200 pounds per ton or more of agglomeration promoting additive may remain on the product coal agglomerates retained on screen 18. This additive is recove~red b~ trans-ferrincJ the agglomerates throucJIl concluit 22 ko a wasllc.~r 2~l wher~ -the aclditive is w~shcd or leached Erom the agcJlorner~tc!s with a fluorocarbon solvent of the charac-ter clescribed akove and introduced into the washer through line 26.
The deslgn of the washer is not critical. It may, as one example, be a countercurrent extractor of the character descriked in U.S. Patent No. 3,941,679 issued r~arch 2, 1976, to Smith e-t al.
The process conditions described in -tha-t patent are directly applicable in stripping or washing the acJglomera-tion promoting additive from the product coal acJ~lomerates in washer 24.
One effluent from the washer consists of product coal agglomerates wetted with the solvent and dispersed in the solvent-additive phase generated in the washer.
This efElucnt is transferred through line 28 to a cen-trifuge 30 to separate -the agglomerates fro~ the solvent ~J - 10 -~3~
and additive. Product coal agglomerates with their accompany-ing burdens of fluorocarbon solvent and in at leas-t the majority of cases, at least some surface ~ater, are trans-ferred through line 32 to an evaporator 34 where at least the fluorocarbon is stripped from the agglomerates. Moisture associated therewith ~ay also be stripped from the coal in evaporator 34.
However, it is not in every case necessary that all, or even any, of this moisture be removed; and it :is an important feature of our invention tha-t an essentiall~
quantitative (99~ plus) recovery of the fluorocarbon can be made without removing the water. It is also important that, if a reduction in product coal moisture content does prove necess~ry, evaporation oE the fluorocarbon solvent can be effected at a fast enough rate to substantially reduce the vapor pressure over and, as a consequence, the cost of recovering the moisture from the coal.
. Suitable evaporatdrs are described in U. S. Patent No. 4,173,530.
Dried agglomerates discharged from evaporator 3 are ready for utilization as indicated by arrow 36.
Vapor generated i.n evaporator 34 flows through line 38 to a condensor-purge unit 40.
The solvent-additive mixture discharged from centrifuge 30 is pumped through line 42 to an evaporator 44 where the solvent is stripped from the higher boiling point agglomeration promoting additive. The additive is trans-ferred through line 41 to an additive storage facility or tank 48 from which it can be recirculated to agglomerator 10 through transfer device 1~.
~3~3f~
., Vaporized parting llquid generated in eva~orator 44 is transferrecl through line 50 to condensor-purge unit 40 where it is combined with the vapor flowin~ to that unit ~-~
through line 38. Condensed, degassed parting li~uid is -~
pumped from unit 40 through line 52 to storage facility tank 54.
Numerous embodiments of our inven-tion have been described above, and that invention may be embodied in still other specific forms without departing fxom the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustra-tive and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all chan~es which come within the meanin~
and range of equivalency of the claims are therefore intended to be ernbraced therein.
, '~'i '-' ''
description and discussion proceeds in conjunction ~ th the appended drawing in which the single figure is a flow diagram of one process for beneficating coal in accord with the principle of the present invention.
Referring now to the drawing, the separation of coal from the mineral matter associated therewith, the sub-sequent agglomeration of the coal particles, and the ejection of mineral matter and water from the agglomerates is carried out in an agglomerator 10 which may be, for example, a homogenizer as described in U.S. Patent ~o. 2,744,626 issued ~ .
December 15, 1952, to Reerink et al; a tumbler as described in U.S. Patent No. 3,471,267 issued October 7, 1965, to Capes et al; or a ball, beater, buhr, cage, Chilean, colloid, disc, distintegrating, hammer, pebble, pendulum, pin, Raymond, rod, or comparable mill.
The separation may be carried ou-t at ~mbient temperature and pressure.
Agglomerator 10 p~ovides mechanical forces which jam the coal particles in the raw coal into agglomerates of - the wanted character and which eject the mineral matter and water from the agglomerates. In addition, it generates .forces which knead or work the agglomerates to expel addi-tional mineral matter and water therefrom.
Also, if a mill type agglomerator is employed, the agglomerator reduces the size of the material fed to it, perhaps liberating additional product coal from the mineral matter to which it is bound, and exposing fresh surfaces on the coal particles. Exposure of fresh surfaces to the agglomerating agent can be important because the agglomera-tion of the product coal particles involves surface active , 2F~6~
phenomena which~ at least generally, operate most efficiently only on freshly exposed coal particle surfaces.
Raw coal and the selected agg]omeration promoting additive are introduced into agglomerator 10 through transfer devices indicated generally by reference characters 12 and 14. Such water as may be necessary to form a slurry wi-th appropriate characteristics is introduced into mill 10 through conduit 16.
The amount of additive we employ is th.~t necessary for an efficient agglomeration o the particles of product coal to be effected. As discussed in the reerences cited above, this can range from G0 to over 200 pounds of additive per ton of coal.
As indicated above, the additive employed in ou~
novel process is a hydrocarbon whlch is soluble in the fluorocarbon used -to recover it. The addi-tive, which must be one with respect to which the coal particles are hydrophobic, will typically be, or include:, a petroleum distillate or solvent; a nitrobenzene; a kerosene; a lubricating, fuel, or residual oil; or a chlorinated biphenyl.
As discussed in copending Cdn. Serial No. 33g,~11, iled November 2, 1979, it is also desirable, in many cases, to add calcium oxide in either hydrated or anhyclrous form to the slurry during the agglomeration process. The calci.um oxide, if employed, is introduced into agglomerator 10 through transfer device 17. From 0.5 to 3 percent of calcium oxide (calculated as CaO) based on the weight of the raw coal is employed. It is preferred that the calcium oxide be dosed or metered to the agglomerator over the period of coal ~30 particle separation and agglomeration.
g _ , . . _ ~ .
-~ 3 3 ..:
Tlle ac~ueous carri~r and mineral mat-ter are dis-charged- from agglol~erator 10 through a screen 18 on which the agglomerates of product coal are retained. This aclueous phase is transferred through conduit 20 to a conventlonal thickener (not shown). Suitable thickeners ~re described in Taggart, HANDBOOK OF MI~ERAL DR~SSING, John r.~iley & Sons, Inc., New York, New ~or~, 1927, pp. 15-0~ -- 15-~6~ rrhe mineral matter consol~da-ted in -the -thickener may be transferred to a refuse heap or landfill, for example;
and the water can be recycled.
Up to 200 pounds per ton or more of agglomeration promoting additive may remain on the product coal agglomerates retained on screen 18. This additive is recove~red b~ trans-ferrincJ the agglomerates throucJIl concluit 22 ko a wasllc.~r 2~l wher~ -the aclditive is w~shcd or leached Erom the agcJlorner~tc!s with a fluorocarbon solvent of the charac-ter clescribed akove and introduced into the washer through line 26.
The deslgn of the washer is not critical. It may, as one example, be a countercurrent extractor of the character descriked in U.S. Patent No. 3,941,679 issued r~arch 2, 1976, to Smith e-t al.
The process conditions described in -tha-t patent are directly applicable in stripping or washing the acJglomera-tion promoting additive from the product coal acJ~lomerates in washer 24.
One effluent from the washer consists of product coal agglomerates wetted with the solvent and dispersed in the solvent-additive phase generated in the washer.
This efElucnt is transferred through line 28 to a cen-trifuge 30 to separate -the agglomerates fro~ the solvent ~J - 10 -~3~
and additive. Product coal agglomerates with their accompany-ing burdens of fluorocarbon solvent and in at leas-t the majority of cases, at least some surface ~ater, are trans-ferred through line 32 to an evaporator 34 where at least the fluorocarbon is stripped from the agglomerates. Moisture associated therewith ~ay also be stripped from the coal in evaporator 34.
However, it is not in every case necessary that all, or even any, of this moisture be removed; and it :is an important feature of our invention tha-t an essentiall~
quantitative (99~ plus) recovery of the fluorocarbon can be made without removing the water. It is also important that, if a reduction in product coal moisture content does prove necess~ry, evaporation oE the fluorocarbon solvent can be effected at a fast enough rate to substantially reduce the vapor pressure over and, as a consequence, the cost of recovering the moisture from the coal.
. Suitable evaporatdrs are described in U. S. Patent No. 4,173,530.
Dried agglomerates discharged from evaporator 3 are ready for utilization as indicated by arrow 36.
Vapor generated i.n evaporator 34 flows through line 38 to a condensor-purge unit 40.
The solvent-additive mixture discharged from centrifuge 30 is pumped through line 42 to an evaporator 44 where the solvent is stripped from the higher boiling point agglomeration promoting additive. The additive is trans-ferred through line 41 to an additive storage facility or tank 48 from which it can be recirculated to agglomerator 10 through transfer device 1~.
~3~3f~
., Vaporized parting llquid generated in eva~orator 44 is transferrecl through line 50 to condensor-purge unit 40 where it is combined with the vapor flowin~ to that unit ~-~
through line 38. Condensed, degassed parting li~uid is -~
pumped from unit 40 through line 52 to storage facility tank 54.
Numerous embodiments of our inven-tion have been described above, and that invention may be embodied in still other specific forms without departing fxom the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustra-tive and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all chan~es which come within the meanin~
and range of equivalency of the claims are therefore intended to be ernbraced therein.
, '~'i '-' ''
Claims (12)
1. A process for recovering coal from a particulate composite in which said coal is associated with mineral matter, said process comprising the steps of: treating said composite in an aqueous carrier with a non-aqueous, organic agglomeration promoting additive with respect to which the coal is hydrophobic to effect a coalescence of the coal particles into product coal agglomerates and the ejection of mineral matter into dispersion in said aqueous carrier; recovering said product coal agglomerates from said aqueous carrier; and washing said product coal agglo-merates with a fluorocarbon in which said additive is soluble to thereby effect a recovery of said agglomeration promoting additive from said product coal agglomerates.
2. A process as defined in claim 1 together with the steps of mechanically separating said product coal agglomerates from said agglomeration promoting additive and said fluorocarbon and thereafter resolving the mixture of agglomeration promoting additive and fluorocarbon into its constituents and recycling said constituents.
3. A process as defined in claim 1 wherein the fluoro-carbon is selected from the group consisting of:
dichlorofluoromethane trichlorofluoromethane 1,1,2,2-tetrachloro-1,2-difluoroethane 1,1,2-trichloro-1,2,2-trifluoroethane 1,1-dichloro-1,2,2,2-tetrafluoroethane 1-chloro-2,2,2-trifluoroethane 1,1-dichloro-2,2,2-trifluoroethane 1-chloro-2-fluoroethane and mixtures of the foregoing.
dichlorofluoromethane trichlorofluoromethane 1,1,2,2-tetrachloro-1,2-difluoroethane 1,1,2-trichloro-1,2,2-trifluoroethane 1,1-dichloro-1,2,2,2-tetrafluoroethane 1-chloro-2,2,2-trifluoroethane 1,1-dichloro-2,2,2-trifluoroethane 1-chloro-2-fluoroethane and mixtures of the foregoing.
4. A process as defined in claim 1 in which the agglomeration promoting additive comprises a petroleum distillate or solvent; a nitrobenzene; a kerosene; a lubricating, fuel, or residual oil; or a chlorinated biphenyl.
5. A process as defined in claim 1 which includes the steps of stripping the fluorocarbon from the product coal agglo-merates and then recovering and recycling said fluorocarbon.
6. A process as defined in claim 1 which is carried out at ambient temperature and pressure.
7. A process for disassociating coal from a composite in which mineral matter is associated therewith and recovering said coal in agglomerated form, said process comprising the steps of:
forming a slurry of said composite in an aqueous carrier; provid-ing a non-aqueous, organic agglomeration promoting additive with respect to which said coal particles are hydrophobic in said slurry in an amount sufficient that agglomeration of the coal can be effected; comminuting the particles of composite while in said slurry to separate the mineral matter from the coal and to gen-erate coal particles having freshly exposed surfaces in a controlled environment; mechanically effecting the coalescence of the coal particles into product coal agglomerates and the ejection of mineral matter and water from the agglomerates into dispersion in said aqueous carrier; recovering said product coal agglomerates from said slurry; and washing said product coal agglomerates with a fluorocarbon solvent in which the agglomeration promoting additive is soluble to thereby recover said agglomeration promoting additive from said product coal agglomerates.
forming a slurry of said composite in an aqueous carrier; provid-ing a non-aqueous, organic agglomeration promoting additive with respect to which said coal particles are hydrophobic in said slurry in an amount sufficient that agglomeration of the coal can be effected; comminuting the particles of composite while in said slurry to separate the mineral matter from the coal and to gen-erate coal particles having freshly exposed surfaces in a controlled environment; mechanically effecting the coalescence of the coal particles into product coal agglomerates and the ejection of mineral matter and water from the agglomerates into dispersion in said aqueous carrier; recovering said product coal agglomerates from said slurry; and washing said product coal agglomerates with a fluorocarbon solvent in which the agglomeration promoting additive is soluble to thereby recover said agglomeration promoting additive from said product coal agglomerates.
8. A process as defined in claim 7 together with the steps of mechanically separating said product coal agglomerates from said agglomeration promoting additive and said fluorocarbon and thereafter resolving the mixture of agglomeration promoting additive and fluorocarbon into its constituents and recycling said constituents.
9. A process as defined in claim 7 wherein the fluoro-carbon is selected from the group consisting of:
dichlorofluoromethane trichlorofluoromethane 1,1,2,2-tetrachloro-1,2-difluoroethane 1,1,2-trichloro-1,2,2-trifluoroethane 1,1-dichloro-1,2,2,2-tetrafluoroethane 1-chloro-2,2,2-trifluoroethane 1,1-dichloro-2,2,2-trifluoroethane 1-chloro-2-fluoroethane and mixtures of the foregoing.
dichlorofluoromethane trichlorofluoromethane 1,1,2,2-tetrachloro-1,2-difluoroethane 1,1,2-trichloro-1,2,2-trifluoroethane 1,1-dichloro-1,2,2,2-tetrafluoroethane 1-chloro-2,2,2-trifluoroethane 1,1-dichloro-2,2,2-trifluoroethane 1-chloro-2-fluoroethane and mixtures of the foregoing.
10. A process as defined in claim 7 in which the agglomeration promoting additive comprises a petroleum distillate or solvent; a nitrobenzene; a kerosene; a lubricating, fuel, or residual oil; or a chlorinated biphenyl.
11. A process as defined in claim 7 which includes the steps of stripping the fluorocarbon from the product coal agglo-merates and then recovering and recycling said fluorocarbon.
12. A process as defined in claim 7 which is carried out at ambient temperature and pressure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/041,063 US4274946A (en) | 1974-04-12 | 1979-05-21 | Agglomeration type coal recovery processes |
| US041,063 | 1979-05-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130260A true CA1130260A (en) | 1982-08-24 |
Family
ID=21914515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA348,868A Expired CA1130260A (en) | 1979-05-21 | 1980-03-31 | Agglomeration type coal cleaning processes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1130260A (en) |
-
1980
- 1980-03-31 CA CA348,868A patent/CA1130260A/en not_active Expired
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